Inhibition by red phosphorus of unimolecular thermal chain-scission in poly(methyl methacrylate): Investigation by NMR,FT-IR and laser desorption/fourier transform mass spectroscopy

The reaction of red phosphorus with poly(methyl methacrylate) under pyrolysis conditions was investigated with a number of physical techniques. A random methyl methacrylate/cyclic anhydride copolymer is formed from atatic PMMA, whereas a random methyl methacrylate/methacrylic acid copolymer is obtained with isotactic PMMA. The backbones of both these copolymers are more stable toward depolymerization than that of PMMA. The flame-retardant activity of red phosphorus with PMMA may arise in part from stabilization of the polymer toward depolymerization via modification of the sidechains.     

Influencing polymer properties by regiospecific complexation

ABA block-copolymers in which the A segments are capable of forming complexes and B is a non-complexing segment, have been used to prepare polymer materials with properties that can be changed by adding a complexing agent. The complex forming segments were poly(ethylene oxide) (PEO), linear polyethylenimine (LPEI) and poly(N-tert-butylethylenimine) (PTBEI). Commercially available liquid ABA block-copolymers, in which A is PEO and B is poly(propylene oxide), were investigated with high molar mass poly(acrylic acid) (PAA) as the complexing agent for PEO. It was found that the mixtures containing 3 to 7 wt.-% of PAA, showed a marked shear-thickening behavior leading eventually to gelation. This was attributed to the transformation of intramolecular polymer complexes, at low shear rates, to intermolecular complexes, at high shear rates, due to the chain stretching of PAA. ABA copolymers in which A is LPEI or PTBEI and B polytetra-hydrofuran (PTHF), were prepared. Complexation of these copolymers with low molecular weight poly-acids or PAA in polar and non-polar solvents as well as in bulk have been investigated. ABA copolymers in which A is PEO and B a PTHF segment were prepared. These block-copolymers show two melting points: one at appr. 55°C, due to the PEO segments, and one at appr. 30°C due to the PTHF. Upon addition of alkali metal salts such as sodium iodide or sodium thiocyanate, complexes with PEO are formed and as a consequence, the melting point of the PEO segments shifts to appr. 160°C. The complexed materials behave as thermoplastic elastomers up to that temperature.     

Heteropoly acid as a novel efficient catalyst for Fries rearrangement

Heteropoly acid H3PW12O40 is a very efficient and environmentally benign catalyst for the Fries rearrangement of phenyl acetate in homogeneous or heterogeneous liquid-phase systems at 100-150 degrees C.     

Physical properties from association models

Equation of state models with a ‘chemical’ contribution that accounts for association and solvation effects, are computationally intensive as they have to solve an internal chemical equilibrium calculation.

Frequently, only the final results of this internal calculation are used in the subsequent evaluation of physical properties from the model. As a consequence, a substantial amount of unneeded work is performed. We show here how the state function minimization in the chemical equilibrium calculation can be utilized to simplify the calculation of physical properties like pressure and chemical potentials and the derivatives of these properties with respect to temperature, volume and composition.     

A Thermodynamic Study of 1-Propanol–Glycerol–H2O at 25°C: Effect of Glycerol on Molecular Organization of H2O

The excess chemical potential, partial molar enthalpy, and volume of 1-propanol were determined in ternary mixtures of 1-propanol–glycerol–H₂O at 25°C. The mole fraction dependence of all these thermodynamic functions was used to elucidate the effect of glycerol on the molecular organization of H₂O. The glycerol molecules do not exert a hydrophobic effect on H₂O. Rather, the hydroxyl groups of glycerol, perhaps by forming clusters via its alkyl backbone with hydroxyl groups pointing outward, interact with H₂O so as to reduce the characteristics of liquid H₂O. The global hydrogen bond probability and, hence, the percolation nature of the hydrogen bond network is reduced. In addition, the degree of fluctuation inherent in liquid H₂O is reduced by glycerol perhaps by participating in the hydrogen bond network via OH groups. At infinite dilution, the pair interaction coefficients in enthalpy were evaluated and these data suggest a possibility that the interaction is mediated through H₂O.     

DMT [(−)-(2<Emphasis Type="Italic">R</Emphasis>,3<Emphasis Type="Italic">R</Emphasis>)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol], a highly efficient host compound for nitroaromatic guests: selectivity,X-ray and thermal analyses

In this work, we reveal that the compound (?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitrobenzene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB?≈?p-NT?>?o-NT?>?m-NT. Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%)?>?NB (30.2%)?>?m-NT (17.1%)?>?o-NT (12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated with the selective behaviour of the host in competition experiments.     

A Polyketide Synthase Component for Oxygen Insertion into Polyketide Backbones

Enzymatic core components from trans‐acyltransferase polyketide synthases (trans‐AT PKSs) catalyze exceptionally diverse biosynthetic transformations to generate structurally complex bioactive compounds. Here we focus on a group of oxygenases identified in various trans‐AT PKS pathways, including those for pederin, oocydins, and toblerols. Using the oocydin pathway homologue (OocK) from Serratia plymuthica 4Rx13 and N‐acetylcysteamine (SNAC) thioesters as test surrogates for acyl carrier protein (ACP)‐tethered intermediates, we show that the enzyme inserts oxygen into β‐ketoacyl moieties to yield malonyl ester SNAC products. Based on these data and the identification of a non‐hydrolyzed oocydin congener with retained ester moiety, we propose a unified biosynthetic pathway of oocydins, haterumalides, and biselides. By providing access to internal ester, carboxylate pseudostarter, and terminal hydroxyl functions, oxygen insertion into polyketide backbones greatly expands the biosynthetic scope of PKSs.     

Total Synthesis and Structural Revision of the Antibiotic Tetrapeptide GE81112A

The total synthesis of the naturally occurring antibiotic GE81112A, a densely functionalized tetrapeptide, is reported. Comparison of spectral data with those of the natural product and the lack of biological activity of the synthesized compound led us to revise the published configuration of the 3‐hydroxypipecolic acid moiety. This hypothesis was fully validated by the synthesis of the corresponding epimer.     

Evolved Gas Analysis‐Mass Spectrometry to Identify the Earliest Organic Binder in Aegean Style Wall Paintings

An organic binder was identified in the painted fragments from the Canaanite palace of Tel Kabri, Israel. Recently dated to the late 18th century B.C.E. by ¹⁴C, Tel Kabri is the most ancient of the Eastern Mediterranean sites in which Aegean style paintings have been found. The application of pigments was suspected to be using an organic binding medium, particularly for the Egyptian Blue pigment. Samples of blue paint were examined using evolved gas analysis‐mass spectrometry (EGA‐MS) in order to overcome the analytical challenges imposed by highly degraded aged proteinaceous materials. Egg was identified as the binder based on the presence of hexadecanonitrile and octadecanonitrile, confirming the use of a secco painting technique. Lysozyme C from Gallus gallus was detected by proteomics analysis, confirming the presence of egg. To our knowledge, this is the earliest use of egg as a binder in Aegean style wall paintings.     

A Metal–Organic Framework with Cooperative Phosphines That Permit Post‐Synthetic Installation of Open Metal Sites

PCM‐101 is a phosphine coordination material comprised of tris(p‐carboxylato)triphenylphosphine and secondary pillaring groups coordinated to [M₃(OH)]⁵⁺ nodes (M=Co, Ni). PCM‐101 has a unique topology in which R₃P: sites are arranged directly trans to one another, with a P???P separation distance dictated by the pillars. Post‐synthetic coordination of soft metals to the P: sites proceeds at room temperature to provide X‐ray quality crystals that permit full structural resolution. Addition of AuCl groups forces a large distortion of the parent framework. In contrast, CuBr undergoes insertion directly between the trans‐P sites to form dimers that mimic solution‐phase complexes, but that are geometrically strained due to steric pressure exerted by the MOF scaffold. The metalated materials are active in heterogeneous hydroaddition catalysis under mild conditions, yielding different major products compared to their molecular counterparts.